"Most of the long-term unemployed in Australia have low skills, and that's their problem," University of Melbourne professor Peter McDonald says.

"But it's not because of migration. And, if anything, migration, by leading to greater investment and so on, is actually creating jobs for that group."

Since 2011, employment in Australia has grown by 730,000 people, and 600,000 of them were new migrants.

Professor McDonald says it has transformed the workplace.

"The Australian labour force would have aged quite a lot without migration. Migration makes a very big difference to the age structure of the labour force by bringing in young workers, whereas all our growth at the moment without migration is with older workers."

The study found, without migration, the number of people under age 55 in the workforce would have slumped by more than 140,000.

But with new workers coming in from overseas, the numbers climbed by more than 450,000.

By contrast, among older workers, there would have been a boost of almost 270,000 without migration, a number only slightly higher with the five-year influx.

But the big growth in migrant-employment numbers has come with an increased risk of workplace exploitation.